This invention relates to an improved illuminated sign, and, more specifically to an improved sign and method for designing a sign that provides bright illumination without a visible presence of undesirable streaks in the illumined lettering or graphics of the sign.
Illuminated signs are used throughout the world to convey information to passers-by. Neon is often chosen for such illuminated signs because of the distinctive, brilliant color and light it emits. Traditionally, neon has been used in the form where tubing is bent into the shape of a word. Manufacture of this type of sign requires the frequently costly services of a skilled glass tube bender. Such signs are also limited in that once they have been created (at considerable expense), they cannot be modified.
Referring now to FIGS. 1, 2, 8, and 9, there are depicted partial-cutaway plan views and cross-sectional side views of illuminated signs, known as grid signs or light-box signs. The general structure of such signs is known in the art. Grid signs are described generally in several early U.S. patents (for example, U.S. Pat. No. 1,813,759 to Thomas Peters, U.S. Pat. No. 2,080,679 to E. D. Vissing, U.S. Pat. No. 2,094,436 to H. R. VanDeventer et al., U.S. Pat. No. 2,046,044 to R. A. Vissing, and U.S. Pat. No. 2,118,385 to J. J. Shively). Such signs are not prevalent in commerce today. As shown in FIGS. 1 and 2, sign 10 comprises essentially a sign frame 14 having a width xe2x80x9cWxe2x80x9d in which are located lengthwise sections of luminous tubing 12 parallel to the width and providing illumination. The sign frame is covered by a sign face 18 having transparent letters 11 outlined by an opaque background 13.
FIGS. 8 and 9 show a light-box sign 50 with fluorescent bulbs 51 and a diffusion faceplate 52. Diffusion faceplate 52 has light diffusion properties and is spaced a sufficient distance from bulbs 51 to diffuse and distribute emitted and reflected light across the plate so the faceplate provides a relatively even light surface. The properties of this diffusion faceplate reduce significantly the amount of light (L2) that reaches the viewer as compared to the amount of light (L1) that is emitted by the bulb and therefore prevents the sign from achieving peak brightness. This loss of light (L1-L2) can be compensated for by increasing the light transmitting properties of the diffusion plate, which in turn typically results in streaks of greater and lesser brightness being more visible.
Luminous tubing 12 and 51 generally has a small diameter relative to the sign width. Therefore, to provide illumination over the complete sign width, numerous lengths of individual tubing are typically used in fluorescent light boxes. To achieve a similar effect with neon tubing, a single tube may be bent in alternating 180-degree curves into an S-shaped pattern with lengthwise sections 15 between curves 42, as shown in FIG. 1. The luminous tubing 12 is electrically attached to an electrical power supply 16. To provide a uniform appearance of light instead of a series of lines, the tubing may be mounted within curved, reflective channels 20 that have a mirrored surface.
A grid sign offers an advantage over signs comprising merely a neon tube bent into the shape of a word, in that a single sign frame 14 may be used with multiple or modifiable sign faces 18 to change the text of the sign as desired. The neon grid signs or fluorescent light boxes having diffusion plates which minimize the amount of light blocked, as described in the aforementioned references, have a disadvantage, however, in that from certain angles between the viewer and the sign, the light shining through the letters forms a streaked pattern, as depicted in FIG. 3. This streaked pattern may make the message on the sign difficult to read. Depending upon the quality of the reflectors behind the tubing, this streaked pattern may appear as a series of dark lines, or may comprise stripes of greater and lesser brightness.
The unilluminated ridges 22 between reflective channels 20 may contribute to the streaked pattern. A key factor in the creation of the streaked pattern is that the curvature of the reflector 20 may not reflect light back to the viewer 30 from the tubing 12 at certain viewing angles, as shown in FIG. 4, but instead reflects the lesser light coming from the direction of the viewer or other less lighted areas.
Some of the references disclosed above discuss ways to address this problem. Patent ""679 describes the presence of metallic reflectors similar to reflectors 20 that reflect the light from the neon tubing in what is xe2x80x9cpractically a sheet of lightxe2x80x9d. Patent ""679 also describes, however, some presence of dark lines or reduced light reflection efficiency associated with each reflector embodiment. Significantly, patent ""679 also refers to means for angling the sign to enable the sign to be more easily read when the observer is above or below the sign, implying that the illumination quality may suffer when the sign is at a vertical angle from the viewer.
Patent ""436 purports to provide a sheet of neon xe2x80x9csubstantially free of the objectionable streaks and of uniform over-all brilliancyxe2x80x9d; however, the reference provides no detail regarding the geometry of the reflectors, so that this claim can be verified. Additionally, the patent claims adjustable means for tilting the sign face at various angles, again suggesting that the sign may have required angular adjustment to facilitate streak-free viewing at certain angles.
The continued pursuit of an ultra-bright grid sign free of the undesirable streaked pattern in the 1930""s and the dearth of such signs in commercial use today are testimony to the desirability and elusive nature of a sign that eliminates the streaked pattern. The present invention provides an illuminated light-box sign and method for designing such a sign that optimizes the dimensional properties of the reflector channels to eliminate or dramatically reduce the streaked pattern without a diffusion plate at all, or that allows the use of a diffusion plate having relatively high light transmission.
In accordance with this invention, there is provided an illuminated light-box sign with reflectors. The sign comprises a frame having a width, a partially transparent face supported thereon, a single or plurality of lengthwise sections of luminous tubing mounted in the frame, and a single or plurality of concavely-curved, reflective channels. The tubing has a tubing inside radius (r) and an inside surface having a reflector-closest edge. Each reflector has an angle of wrap (xcex2) and a concave surface having a tubing-closest edge positioned at a distance (d) from the tubing inner surface reflector-closest edge. Each channel has a substantially semi-cylindrical shape with a radius of curvature (R). The improvement comprises each channel having an angle of wrap (xcex2) of about 80% to about 150% of the value (xcex2) that satisfies the following equation:             1              sin        ⁢                  (                      β            2                    )                      +          2      ⁢              (                              R            r                    -                      d            r                    -          1                )            ⁢              cos        ⁢                  (                      β            2                    )                      =            R      r        .  
The invention also comprises a method for designing an illuminated grid sign or light box having a single or plurality of lengthwise sections of light-emitting luminous tubing and a single or plurality of concavely-curved reflective channels, each positioned to reflect a portion of the light emitted by one of the lengthwise sections. The method comprises selecting a reflective channel radius (R) and the luminous tubing, the tubing having an inside radius (r) and an inner surface having a reflector-closest edge. Then, the distance (d) between the tubing inner surface reflector-closest edge and a tubing-closest edge of the reflective channel adjacent thereto is determined. Finally, the reflective channels are formed to be substantially semi-cylindrical with a radius (R) and angle of wrap (xcex2) as described above.
The method preferably comprises selecting values for the luminous tubing inside radius (r), the distance (d), the reflective channel radius (R) and angle of wrap (xcex2) that minimize visible streaks of brighter and less-bright illuminated regions in the sign.